Methods have been established to characterize and quantify sub-visible particulates in injectable drug products. See United States Pharmacopeia <788> Particulate Matter in Injections. However, the United States Pharmacopeia-recommended assays for assessing sub-visible particulates in injectable drug products are not applicable to cell therapies, as cells themselves can be considered particulates. Accordingly, there remains a need in the art for methods of quantifying sub-visible particulates in cell cultures.